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However, because a soil material or "baked zone"was observed at the <br /> contact between the dacite and sedimentary rocks, and because the <br /> dacite intruded the Fountain Formation, it was assume that the <br /> differential movement would have resulted in a reduced shear strength <br /> along the contact. A residual shear strength was assumed for <br /> characterizing this contact. Samples of the contact materials along the <br /> northern-most highwall of the quarry were collected for torsional ring <br /> shear testing to estimate the residual friction angle. The ring shear test <br /> results indicate a residual friction angle of about 20 degrees, which was <br /> considered in the stability analysis. The stability analysis considered <br /> kinematic, limit equilibrium block stability, and global stability analyses. In <br /> general, the orientation of these features, perpendicular to the exposed <br /> face, and their high dip angles reduce their impact on the stability. <br /> 6. Several seeps and areas of perched subsurface water were described in <br /> the report. <br /> o Have the areas of seeps and perched water been analyzed as <br /> they pertain to stability? <br /> o Has a sensitivity analysis been done for varying groundwater <br /> levels in the highwall? <br /> Response: <br /> To account for the observed seeps and perched water, groundwater <br /> pressures in the stability evaluation were modeled by using an ru <br /> coefficient. The r„ coefficient is defined as the ratio of the pore water <br /> pressure felt along a potential failure surface to the weight of the rock <br /> overlying that same surface. This allows the modeling of slopes with a <br /> perched a water table (as opposed to a groundwater table). The analysis <br /> used an r„ coefficient of 0.1 which effectively models a perched water <br /> height that is (0.1x155/62.4) or 25 percent of the height of the overlying <br /> rock. <br /> 7. Seismic influences were not included in the kinematic or slope stability <br /> analysis. <br /> o How are seismic conditions evaluated as they pertain to stability of <br /> the slopes? <br /> Response: <br /> The slope stability analyses, for the both sliding block and global rock <br /> mass analyses, evaluated both static and pseudo-static loading <br /> conditions. The pseudo-static analyses used a seismic coefficient to . <br /> model stability under seismic loading conditions. The slope templates in <br /> hdrinc.com 8 <br /> 1670 Broadway,Suite 3400,Denver,CO 80202-4824 <br /> (303)764-1520 <br />